Silver alloys



Patented Aug. 25, 1936 PATENT OFFICE 2,052,142. SILVER ALLQYS Edward F.Kern, New York, N. Y., asslgnor to {The American Metal Company, Limited,New

York, N. Y., a corporation of New York No Drawing. Application August20, 1935, I Serial No. 36,962

'2 Claims. (01. 75-173 This invention relates to the production oftarnish-resisting silver alloys of a fineness equivalent to sterling 925and standard quality 900 fine, as'well as the composition of othersilver 5 alloys possessing tarnish-resisting properties.

It is well-known that silver alloys and articles made of silver whenexposed to the atmosphere or when in contact-with substances containingsulfur assume a darkened colorknown as tarnish.

10 The object of this-invention is to provide silver alloys of finenessofsterling quality and other-' wise which possess tarnish resistingproperties and also which may be readilyunade into articles whichpossess sufllcient hardness to withstand the i5 usual wear and tear. I

The invention comprises the novel compositions and component mixturescomprised in such compositionaspecific embodiments of which aredescribed hereinafter by way of example only 2 and in accordance'withwhat I now consider the preferred manner of practicing the invention.

This application is a continuation in part of my copending applicationSer. No.'739;295, filedv August 10, 1934.

. The invention comprises a'homog'eneous tarnish-resisting silver-tinalloy, with said component metals ranging respectively from 85 to 93%and from 3 to 14%, totaling not more than 99% and not less than 94% ofthe alloy 30 and silicon in an amount not exceeding 1% and holding insolid solution as the remainder of the alloy one or more workabilitycontrol metals, cadmium, zinc, antimony, nickel-chromium alloy, copper,manganese, selected in such amounts as 35 will insure to the rsultingalloy a Brinell hardness of not less than 36. It also includes such analloy containing silver about 85 to 93%, tin about 3 to 14%, and notmore than 1% of'silicon. The amount of silicon'used is preferably suchthat up to about 0.7% is found in the resulting finished alloy. Theproportion ofsilicon may exceed 0.7% up to 1% if desired. A certainamount of silicon is aptto be 'lost in melting depending on thetechnique 45 employed in its addition and it is, therefore, well to adda somewhat'larger amount thereof to the mixed melt than expected in theresulting alloy. As stated this additional amount will depend onthe'technique employed and can be readily deter- 50 mined for a givencase by making one or more melts and observing the resulting amount ofsuch metal obtained in the finished melt. The proportions above givenproduce homogeneous solid alloys. The proportion of copper should notexceed about 3.5%. In preparing the above alloys it is important thatthey be substantially homogeneous throughout. The proportions givenabove produce homogeneous solid alloys. Heterogeneous combinations donot possess the desired properties and I, therefore, have selected the 5homogeneous compositions given.

- As regards thespecific effect of the metals present in silveralloysthe properties were determined by testing a series of the alloys.Tin forms homogeneous solid solution alloys with silver up 1' to 15% tinand 85% silver. ,Tin increases the hardness and lowers the melting pointof the resulting alloy. Other elements as specified above imparttarnish-resisting properties to the alloy and also increase the hardnessof the resulting'l5 alloy.

The results of the tests demonstrated that the silver-tin alloys aremoretarnish-resistingthan the silver-zinc and silver-antimony alloys.The inclusion of small amounts of silicon, cadmium, zinc, antimony;manganese, copper, or nickelchromium alloy in silver-tin alloysincreases their tarnish-resisting properties. Silicon added to alloys ofsilver-tin with small amounts of cadmium, zinc, antimony and copperfurther increase the tarnish-resisting properties and hardness.

Cadmium, zinc, antimony, copper, manganese and nickel-chromium alloyadded to silver-tin alloys control the workability of the resultingalloys.

The compositions made upembodying the metals indicated above were testedto determine their tarnish-resisting properties as follows:--A smallcast block of the composition to be tested was rolled into sheets,highly polished and covered by a. water solution of ammonium sulfidecontaining an excess of free sulfur. This solution of ammonium sulfideand sulfur was selected from a number of tarnish-producing materials, asthe pressions N/lO and N/ 100 are intended to designate respectively10th normaland 100th normal solutions. In accordance with the standardprac-' tice a normal solution is one containing an equivalent weight ingrams of the substance dissolved in one liter of water or'other solvent.The specimen was kept in contact with this solution for five minutes,then washed and dried. The tarnish was-then observed on the specimen.When identical specimens'were exposed to the.atmosphere for severalmonths, the tarnish-resisting eflects observed corresponded tothoseobtained v less or greater than sterling silver.

I give below a series of alloys prepared in accordance with myinvention, together with the results of the above tarnish test and theBrinell hardness testmade on the alloy as cast.

Example Brinell Composition oi mixhues-Melted-Psrts by weight hardness f90 silver, 9 tin, 1 silicon 90 silver, 9.3 tin, 0.7 silicon 89.5 silver,8.75 tin, 1.65 cadmium, 0.1 silicom; 88.6 silver, 8.5 tin, 2.5 cadmium,0.4 silicon... 90 silver, 6.8 tin, 2.5 cadmium, 0.7 silicon. 90 silver,8.3 tin, l cadmium, 0.7 silicon 90 silver, 8. n, 1.5 cadmium, 0.3silioon 90 silver, 'n, 1.5 cadmium, 0.4 silicon. 90 silver, cadmium, 0.7silicon. 90 silver,

90.3 silver, 87.5 silver, 90 silver, 6. 90 silver, 6. 92.5 silver, 90silver, 5. 90 silver, 8. 90 silver, 7. 90 silver,

1.5 cadmium, 1 silicon... 1.5 cadmium, 0.4 silicon cadmium, 0.5 silicon2.9 cadmium, 0.3 silicon.

ban"

2 7 cadmium, 0.7 silicon .2cadmiuin, 0.3 silicon.. 3

.8 cadmium, 0.7 silicou.- zinc, 0.7 silicon .5 zinc, 0.7 silicon...-

U seeass:

.75 zinc, 0.75 silicon 0.7 sllicon.- 0.5 silicon.. 0.7 silicon. no, 0.7silicon.

.8 5 copper, 0.5 silicon. 5 copper, 1 silicon 75 copper, 075 silicon n,3.25 copper, 0.5 silicon n, antimony, 0.3 silicon n, 1 antimony, 0.2silicon tin, 1.5 antimony, 0.3 silicon in, 1.3 antimony, 0.7 silicon 90silver, 90 silver, 90 silver, 8. 90 silver, 8. 90 silver, 8

ti i

The alloys prepared as indicated in the above examples all showed byappropriate tests that they were substantially homogeneous alloys, beingsubstantially free from heterogeneous structure. Each of the alloys ofthe above examples, when subjected to the ammonium sulfide and sulfurtests indicated above, had a tarnish-resisting property capable ofresisting such treatment substantially without appearance of tarnish.Sterling silver and standard silver andvarious other silver alloys whensubjected to this test showed glass, and charcoal.

appreciable tarnish. The silver employed in the above meltswas a finecommercial electrolytic silver as crystals of a high grade of purity andthe other metals were also commercial products of high purity.

The following process is carried out in forming the alloys of the metalor metals with silver and tin:-

The alloys are prepared by melting the weighed amounts of electrolyticsilver and the other constituents under a fiux of for example borax, orThe molten mixtures are thoroughly mixed, then cast in the usual manner.When silicon is made a constituent of the alloy, it may be added eitheras previously prepared alloys, or the silver alloy of silicon may' greatdetail and with respect to certain preferred embodiments thereof, I donot desire to be limited to such details or embodiments. since manychanges and modifications may be made and the invention embodied inwidely different forms without departing from the spirit and scopethereof in its broader aspects. Hence I desire to cover all equivalentsand all modifications and forms coming within the language or scope ofany one or more or the appended claims.

What I claim as new and desire Letters Patent, is:-

1. A homogeneous tarnish-resisting silver-tin alloy with said componentmetals ranging respectively from 85 to 93% and from 3 to 14%, totalingnot more than 99% nor less than 94% to secure by ,0! the alloy, withsilicon not exceeding about 1.0%

